Implantable medical devices (IMDs) are well known for providing a variety of therapies to humans. For example, implantable cardiac defibrillators are used to monitor the electrical activity of the heart of a patient, detect ventricular fibrillation, and in response to that detection, deliver appropriate therapy pulses to restore a normal heart rhythm. Implantable neurostimulators have been used to stimulate the spinal cord and brain for a variety of treatments, including the treatment of chronic pain and the treatment of peripheral vascular disease. Implantable pacemakers generate and apply electric stimuli in the form of pulses to the tissue of a heart to control the timing of the contractions of the heart.
The above-described IMDs, and other similar devices, utilize an internal power source, or electrochemical cell, to provide the power required for a desired application. Implantable cardiac defibrillators also use an electrolytic capacitor which is charged by the internal power source and subsequently discharged in order to provide electrical pulse therapy. The electrolytic capacitor includes an anode, a cathode, and electrolyte disposed therebetween. Typically, the anode is constructed from metal, such as aluminum, tantalum, titanium, or other suitable metals capable of forming anodic oxides upon anodization. The cathode may be configured as a coating on a metal, for example, graphite on titanium as disclosed in U.S. Pat. No. 7,002,790, and may be applied to the metal by, for example, chemical vapor deposition, physical vapor deposition, or spraying.
Alternatively, the cathode may be configured as a sheet metal which has been treated, for example by etching, in order to obtain a larger surface area.
In instances in which a high capacitance, low resistance capacitor is preferred, silver vanadium oxide may be used to coat the cathode. It has been found that silver vanadium oxide alone yields relatively high capacitance and that the capacitance of compressed pellets consisting of silver vanadium oxide powder can be significant. However, the electrical conductivity of silver vanadium oxide pellets is comparatively low, resulting in an unacceptably high equivalent serial resistance (“ESR”) of the finished capacitor. In addition, forming a durable coating of silver vanadium oxide powder on a metallic substrate without diminishing the capacitance is relatively difficult.
Accordingly, there is a need for a method of producing a silver vanadium oxide coating on a cathode that yields high capacitances and low ESR values in order to render the electrode suitable for use in a high-voltage defibrillator capacitor, where capacitance values of greater than approximately 10 mF/cm2 are typically preferred. Additionally, it would be desirable for the method to be relatively simple and cost-effective to use. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.